Simple pin-back for circus employee's I believe and something not seen very often. Based out of Sheboygan Wi from the late teens through the late 30's.

"The Lindemann Brothers Circus gave its first performance in 1918. Well established by 1925, the Lindemann adopted the name Seils-Sterling, and their circus became one of the country's greatest motorized shows. "

Additional info can be found here: http://www.elephant.se/location2.php?location_id=728